Telephone system



L. J. BOWNE March 9, 1937.

TELEPHONE SYSTEM 2 Sheets-Sheet 1 Filed Dec. 29, 1934 o nlfs/ /Nl ENTOR 1.. J. BOWNE ATTORNEY March 9, 1937. L. J. BOWNE TELEPHONE SYSTEM Filed Dec. 29, 1934 2 Sheets-Sheet 2 III . QQN

3w mum Qw 9w new 8m 8m lNl/E/VTOR L. J. BOWNE ATTORNE Patented Mar. 9, 1937 UNITED STATES TELEPHONE SYSTEM Langford J. Bowne, Howard Beach, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a. corporation of New York Application December 29, 1934, Serial No. 759,644

18 Claims.

This invention relates to telephone systems and particularly to arrangements for preventing acoustic shocks or high potential signals from penetrating to operators or subscribers apparatus.

An object of the invention is to simplify a telephone system in which terminal apparatus is to be protected against acoustic shock caused by high potential signals from external sources or that are transmitted over telephone lines for other signaling purposes, for example, when said telephone lines are used in railway train dispatching systems.

Heretofore systems have been provided in which telephone lines have been equipped with shock absorbing means to protect terminal equipment from excessive voltages and yet permit signaling currents of the usual telephone signal voltages to be transmitted out over the line. A system along these lines has been disclosed in my Patent No. 1,987,430 of January 8, 1935. In this patent a system is shown in which shock absorbing means are provided for the terminal apparatus against train dispatching signals and other excessive high voltage disturbances incoming on a line while ordinary ringing signals having voltages usual in telephone circuits are permitted to be repeated past the said protecting means from the terminal apparatus out over the line.

It is a feature of the present invention to provide in systems of this kind protecting means for the terminal apparatus against disturbing voltages such as high potential low frequency signals, used in train dispatching systems or excessive voltages caused by speech ciurents of abnormal levels or from other sources, while ordinary ringing signals having voltages usual in telephone circuits are permitted to pass through the circuit from the terminal apparatus to the line without interference from the shock absorbing means. The shock absorbing means includes condensers and a regular repeating coil employed for transmission purposes in the circuit, and the arrangement is such that the signals by-pass the condensers but not the repeating coil.

Another feature is the arrangement of the usual repeating coil and condensers in series with one set of windings thereof of such characteristics that said condensers and repeating coil will serve as the shock absorbing means for high voltage low frequency signals incoming over the line.

Another feature is the arrangement of an alternating current relay bridged across the other set of windings of the repeating coil which is responsive to ringing current outgoing from the terminal apparatus and circuit connections controlled by said relay to shunt the condensers through resistances to by-pass the ringing signals across the condensers so that such signals may be repeated through the repeating coil out over the line without being afiected by said condensers.

Another feature is the arrangement of other condensers in series with a line conductor and shunted by a retardation coil and a plurality of non-lineal resistance elements arranged in cascade formation bridged across the line conductors with one side of said elements connected at a point between said other condensers, said elements comprising non-lineal resistances of the kind in which the resistance decreases with rising potential, such as copper-oxide rectifiers or other similar devices. Said arrangement of condensers and resistance elements serves to shunt abnormal voltages within the voice frequency range occurring in the speech currents transmitted in either direction over the line, while speech currents within the normal levels pass unobstructed through the condensers, and the arrangement of the shunting retardation coil serves as a path for ringing current signals in either direction unobstructed by the condensers and resistance elements.

A modification of this latter feature is an arrangement of condensers in series in each conductor, each series shunted by a retardation coil and resistance elements connecting a point between the condensers in one conductor with a point between the condensers in the other conductor.

Referring now to the drawings:

Fig. 1 shows in a general diagrammatic form the invention applied to a train dispatching system using telephone lines;

Fig. 2 shows the terminating telephone equipment at the calling end of a telephone line;

Fig. 3 shows the terminating telephone equipment at the called end of, a telephone line used for train dispatching; and

Fig. 4 shows the terminal telephone equipment at the called end of a dispatchers line, said equipment being arranged for installation in a telephone switchboard.

-Referring now particularly to Fig. l, the various features have been applied as stated to a train dispatching system using telephone lines for the connecting line between terminating stations and way stations comprising a train dispatching apparatus. In the particular system illustrated in this figure, I represents a so-called dispatchers line while 2 represents a socalled message line. The message line is ordinarily used for dispatching purposes only when the dispatchers line is temporarily disabled. The dispatchers line is provided at the calling station A with the train dispatchers telephone set 3 and the usual train dispatching calling apparatus 4 represented in diagrammatic form and employed by the train dispatcher for selecting way stations. Such systems usually comprise a key for aiiecting the terminal apparatus. apparatus at i5 is also arranged. so that it may circuits.

sending code signals and selectors and suitable circuit. arrangements for the transmission of code signals. At the way stations, such as 5, 5 and 7, train dispatching signaling selector apparatus is provided, while at the receiving station B, the line is equipped with train dispatching selector apparatus and suitable circuit arrangements for terminating the dispatchers line on a telephone switchboard with the necessary acoustic shock absorbing means which is a feature of this invention. If the message line 2 is to be used to call between the stations, it is so arranged that a code calling key equipment is provided at it for calling the Way stations i l, 52 and E3 or the terminating apparatus at the called station B as shown at The way station apparatus ll, l2 and it may be the same as way station apparatus 5, 5, or 1. A terminating station l6, similar to station 5 5, may also be provided for the establishing of telephone connections between station A and this station 56, or between station B and this station it. The dispatchers line i and the message line 2 may be connected and serve as side circuits of a phantom line circuit terminating at stations A and B in terminal apparatus l3 and it, respectively. This phantom arrangement is not shown in detail, but is merely indicated to illustrate the possibilities or" the application of the ieatures of this invention to various types of systems. ie various features of this invention are embodied in the terminal apparatus at stations A and B at l8, l5, l6 and 29.

on lme 2 possibly by some disorder due to the connection of the phantom line or any other disturbances. Likewise, the terminal apparatus at 15 and i6 must be arranged to prevent train dispatching signals of the same character from The terminal be called by train dispatching signals transmitted from station A and equipment it and these signals are translated into ordinary ringing signals for the calling of the terminal apparatus at this end. Shock absorbing equipment may also be provided at 5 for the prevention of train dispatching signals affecting this terminal apparatus. The terminating station it is equipped with these protective and translating devices the same as station 55. Terminal apparatus l8 and !9 are not shown in detail, but may be arranged for sending and transmitting ordinary ringing signals over the phantom derived from the side If either of the side circuits are used for train dispatching signals, then these phantom terminal apparatus may be protected from acoustic shock from such signals by shock absorbing means.

The arrangement of the invention as shown in Figs. 2, 3 and 4 will now be described. Figs. 2 and 3 show the terminal apparatus of the message line 2 at stations A and B respectively. Fig. 2

illustrates the equipment it of Fig. 1, while Fig.

3 serves to illustrate both the equipments at 55 and iii of Fig. 1. Fig. 4 shows the apparatus at 26 and illustrates a circuit method of terminating the dispatchers line i on a telephone switchboard including the necessary shock absorbing equipment. To illustrate the features of this invention, there will be described first a call from the calling station A at l0 over line 2 to call the terminal apparatus l5 at station 33 and the various functions caused thereby such as the translation of the train dispatching signals into ordinary ringing signals at the terminal apparatus [5 and the ringback signal caused thereby to be received at the calling station A by the terminal apparatus of line 2. A description will also be given of signaling between terminal apparatus at stations l5 and it after said stations have been connected up for telephone purposes, of a call from station B to station A, and also of the operation of the terminating circuit Fig. 4 at Referring now to Figs. 2 and 3, if the call is made from the calling station. A at ll] over line 2 the calling operator inserts plug 30 into jack 3! and thereby causes the operation of relay 33 over an obvious circuit closed by the contacts of jack 3!. Relay 33, in operating, provides a connection from ground for the lower spring of the train dispatching key 3 by means of which the operator may signal out over the line. The operator may now ring the desired station or terminal apparatus at station 13 by operating the key St to send the desired code. Although only one key has been shown, it should be understood that in ordinary equipment of this kind, a number of keys may be supplied, each one having a different code. The operation of this key is such that the connections between the contacts are established on the return of the key to normal when a circuit is completed for the operation of relay $5 from battery through the winding of relay 45 and upper and lower contacts of key 3 to ground on the contacts of relay 33. Relay d5 is slow in releasing so that it will remain operated while the code pulses are being sent. Relay $5 in. operating closes a circuit from ground on the contacts of relay 33 through the lower and upper springs of key 3% over conductor 53 through upper operated make contacts of relay 45, righthand windings of repeating coil Lid, lower operated' make contacts of relay &5 to conductor 51 which terminates in the usual special signal apparatus arrangement merely shown in diagrammatic form as a rectangle dd. Ground is also connected to lead 52 which also terminates in the signalling apparatus 49, via middle and lower springs of the key 34. These ground connections on leads 5! andliZ cause the signal apparatus it to connect high potential signals to leads 5% in accordance with the code selection on key (it controlled through the opening and closing of the connection for lead 52 through the'two lower contacts of key 3 1. Relay &5 in operating also disconnects the right-hand windings of repeating coil i l from line 2. Current impulses over leads 5d are transmitted through the left-hand windings of repeating coil it by induction to the right-hand windings of this coil to line 2.

A part of said current impulses transmitted to line 2 is shunted through condensers fill and id to the operators telephone set 54% so that the operator may listen to the code signal that is being sent out. This shunt path may be traced from condensers ll and 43, inductively through the windings of repeating coil 34 including condenser 55, retardation coils 3'5 and d8, shunted, respectively, by condensers 39 and as in series, and by condensers ill and 52 in series, by induction through the windings of repeating coil 35 including condensers 55 and 5?, thence over the ing key 53 to cperators telephone circuit 5 The protecting means for preventing the audible components of the high potential low frequency signals from being transmitted to the operators telephone set 55 in excessive volume to produce undesirable acoustic shocks, resides in the use of the non-lineal resistance elements 43 bridged across the tip and ring conductors, and the circuit arrangement hereinafter described. The said elements, as hereinbefore stated, may be composed of rectifiers oi the kind in which the resistance decreases with rising potential arranged in cascade formation. Since this decrease in resistance is a unidirectional effect, the non-lineal resistances are composed of parallel elements poled oppositely so as to be effective for current impulses in either irection. Assuming that an impulse of audible frequency and of undesirable high potential is transmitted through repeating coil towards operators telephone circu said impulse will be first transmitted through condensers id and 42 to the mid-points 59 and 68 between condensers 33 and to, and ll and d2, respectively. At this point, the high potential will cause the normal resistance of the elements 63 to decrease rapidly, thereby eifectively shunting the said high potential current impulse and preventing it from reaching the operators telephone set in sufiicient magnitude to be disturbing. Rectifier unit 33 is, however, so constituted that it acts as a high resistance shunt to the low potentials of the voice currents of ordinary conversation and accordingly causes only a negligible attenuation. The retardation coils 3? and which bridge condensers 3d and and and 32, respectively, are of comparatively low impedance to low frequency signaling currents, but of high impedance to currents of audible frequency and consequently are an eiiective barrier to the transmission of the aforesaid high potential disturbances. The equipment of Fig. 2, in addition to suppressing excessive amounts of audible frequenoy components of the train dispatching sigis accomplished by the use of low capacity answerback condensers ll and 3 and of repeating coil all of which are of high impedance to low frequency signaling currents. The high potential low frequency code signals incoming at station 3 to the terminal apparatus i5 will be received the usual train dispatching signal apparatus shown by means of a box till (Fi 3). This apparatus is so arranged that the code causes a ground to be applied to the lead llii, thereby operating relay is! over an obvious circuit from battery. Relay E92 connects ground and ringing current through its operated front contacts to re lay 533 through condenser i8 3. Relay let operates and closes an obvious circuit through lamp 535 which lights. It should be noted here that the train dispatching signals have no eiiect on the terminal apparatus as the tip and ring conductors are open at contacts of relays E and l 55 and connected by high impedance answerbacl: condensers lot and H8. Relay H32 releases at the end of the signaling period as the ground connection on lead till is removed from the train dispatching signaling apparatus as it is restored to normal. Audible ringing tone is sent back from this circuit via condensers 16?, 2%, E35, E35,

conductor l repeating coil 52?, including condenser i23, condensers and H8, and repeating coil to line conductors i225 and oi line 2. This audible answer-back signal is returned over line 2 to the sending station at A through he back contacts of relay &5, repeating coil G l, including condenser 55, condensers 3&3, ll and 22, repeating coil 3, including condensers 55 and 5?, jack 3i, plug 3%, key 53 to operators telephone set The rectifier unit :33 has no appreciable attenuating efiect on this answer-back signal as the impressed potential of the signaling current in this case is insuiiicient to cause a breakdown of the resistance of said rectifier unit To answer this call, the operator on seeing the lamp Hi5 lighted, inserts a plug lid in the jack i ll and thereby closes the circuit through the sleeve terminals for the operation of relay 296 which connects the tip and ring conductors through for talking, completing the conversational circuit between operators and 552. In case any disturbing high voltage signals are received over the line while this connection exists, such as, for example, might happen in case of signaling a way station by train dispatching signals, the operators telephone set H2, if connected at this irne, will be protected from acoustic shocks by the non-lineal resistance elements E l S, which are similar to the non-lineal resistance elements :33 of Fig. 2, and the function of which was hereinbefore described.

The terminal apparatus 15 is provided for sending low potential ringing signals.

usual ringing hey its an thereby cause e operation of the ringing relay 55 over a CilClJiG traceable from the made contacts of hey i through contacts or" plug iii and jack 2 i, u

. and lower back contacts of relay loft retardation around condensers I39 and H8 in multiple and 1 l l 8 and i if) in multiple, respectively, thereby providing low impedance paths for the low frequency signaling current.

From junction points E28 and l29, the low frequency signaling current that operated relay 5 it? passes by induction through the windings of repeating coil and condenser thence through shunting resistances lit and ll'i, windings of repeatin of line 2.

If the operator at H2 is to be recalled by a resignal from, for example, the terminal equipment 36, the signal current is transmitted over the line and causes the functioning of a signal which is observed by the op rator at Hi2. This signal current comes in over conductors i25 and iQC, passes by induction through the windings of repeating coil 42 condensers and till, and H3 and H8, each pair in multiple through the operated contacts of relay 5 b induction through windings of repeating coil 22 including condenser E23, winding of relay lid and condenser 27. Relay H5 operates and shunts with resistances i it and i ll, multiple condensers we and lid, and HS and ill}. naling current now passes through resistances Iii? and ill and condensers i ls and lid, and iii? and ill}. From junction points 528 and E29 said signaling current passes through retardation coil it i, over conductor E26, through normally closed coil I25 to conductors and The sig-' If the operator at H2 desires to call, he will operate his contacts of relay I02, through condenser I04 and winding of relay I03, which operates and lights lamp I 05 through an obvious circuit. The operator now responds as hereinbefore described in connection with the operation of the circuit with train dispatching signals. Non-lineal elements H3 are ineffective in shunting the ringing current that operates relay I03, since condensers I and I3I are of such high impedance to the low frequency signaling current that the voltage impressed across the elements I I3 is not sufiiciently high to break down its resistance.

The description hereinbefore given in connection with the apparatus at I0 as shown by Fig. 2 covered a call outgoing over the line toward the apparatus at I5 as shown by Fig. 3. A call proceeding from Fig. 3 to Fig. 2 will now be described. The operator H2, desiring to signal the operator 50, operates the ringingkey H0 which causes the apparatus of Fig. 3 to function as hereinbefore described to cause low frequency ringing current to be transmitted over conductors I25 and I23 of line 2 to the apparatus at I0 as shown by Fig. 2. The current from line 2 comes in on conductors GI and 62 and passes through the back contacts of relay 45, thence by induction through the windings of repeating coil 40 and condenser 55. From repeating coil 00 the ringing current passes through retardation coils 31 and 38, which are of low impedance to the low frequency current. However, condensers 39 and 00 and M and 42 are of comparatively high impedance to said ringing current. Consequently, the ringing current voltage applied across junction points 50 and 00 is so reduced by the aforesaidcombination of retardation coils and condensers as to be ineffective in causing an appreciable reduction in the resistance of the rectifying device 03, and thus as described also hereinbefore in connection with Fig. 3, the shunting eifect of rectifier 03 on the ringing current is negligible. The ringing current now passes through the right-hand windings of repeating coil 36, condenser 63 and the winding of relay 35, which operates and closes an obvious circuit through the lamp 32, which lights. The operator at 50 now responds by inserting plug 30 into jack 3|, thereby establishing a conversational connection with the operator H2.

The operation of the equipment shown in Fig. 4 will now be described. This arrangement is installed at 20 (Fig. 1) to enable an operator at station B to answer and originate calls in connection with the dispatchers line I. On an incoming call the train dispatching selector apparatus diagrammatically shown as a rectangle 200 will function and cause the bell associated with it to operate and signal the operator. In response to this signal operator 203 inserts plug 20! into jack 202, thereby establishing a conversational connection with the calling operator on line I. This connection may be traced from conductors 204 and 205, which connect to the corresponding conductors of line I, through condensers 206 and 201, repeating coil 208 and condenser 209, condensers 2I0 and 2H shunting retardation coil 2I2, thence through the contacts of jack 202, plug 20I and ringing key 2I3 to the operators telephone circuit 203. During the interval that the operator 203 is thus conversing over the dispatchers line, high potential disturbances of audible frequency from said line may pass through repeating coil 208 toward the operator 203. These disturbances, however, do not produce acoustic shocks because of the attenuating effect of the shunting non-lineal resistance elements 2I4 which consist of a non-lineal resistance such as the elements 43 or I i3 and which decreases in value rapidly with increase in voltage, and functions in the manner hereinbefore described in connection with Figs. 2 and 3. If the operator 203 desires to originate a call over the dispatchers line I, plug 20I is inserted into jack 202. The operator then listens on the line and finding that it is not busy talks directly to the sending station or dispatcher. If the call is for another station on line I, the sending station on the request of the operator 203 signals the required station. During the period of signaling operator 203 continues to listen until the called station answers. Repeating coil 208 is so designed that it effectively blocks the passage of the low frequency train dispatching signaling current and the elements 2M absorb any high potential currents of audible frequency that may be present, thereby enabling the operator 203 to listen without experiencing discomfort from acoustic shocks.

What is claimed is:

1. In a signaling system, an exchange, a line terminating at said exchange, means in said line for protecting said exchange against high potential low frequency current signals and against abnormally high potentials within the voice frequency range and for passing normal potentials within the voice frequency range to or from the exchange, and means responsive to low potential ringing frequency signals from the exchange for partially eliminating said protective means from the line to permit the free passage of said ringing frequency signal out over the line.

2. In a signaling system, an exchange, a line terminating at the exchange, means in said line for protecting said exchange against high potential low frequency current signals on the line and means responsive to low potential high frequency current signals from the exchange for partially eliminating said protective means from the line to permit the free passage of said low potential high frequency signals to the line.

3. In combination, a transmission line, a protective device associated therewith for disabling high potential low frequency signals incoming over the line, and means responsive to low potential current signals of a higher frequency for partially shunting said protective device.

4. In combination, a transmission line, a protective device associated therewith for disabling high potential low frequency signals incoming over the line, resistances, and means responsive to low potential high frequency current signals for shunting a portion of said protective device with said resistances.

5. In combination, a transmission line, a protective device comprising a repeating coil and condensers in series with one set of windings of said repeating coil, and means responsive to low potential high frequency signals for shunting said condensers.

6. In combination, a transmission line, a protective device comprising a repeating coil and condensers in series with one set of windings of said repeating coil, resistances, and means responsive to low potential high frequency signals for shunting said condensers with said resistances.

7. In combination, a transmission line, a protective device associated therewith for disabling high potential low frequency signals incoming over the line, a relay associated with said line responsive to low potential alternating current signals of higher frequency, and means responsive to the operation of said relay for partially shunting said protective device to permit free passage of said low potential signals over said line.

8. In a transmission system, a line having two incoming and two outgoing conductors, a repeating coil having primary windings in series with said two incoming conductors and secondary windings in series with said two outgoing conductors, condensers in series with said incoming conductors, the windings of said repeating coil and the condensers having such electrical characteristics that high voltage low frequency signals incoming over the incoming line conductors will indu e a negiigible current in the secondary winding of the repeating coil and the two outgoing conductors.

9. In a transmission system, a line having two incoming conductors and two outgoing conductors, a repeating coil having primary windings in series with said two incoming conductors and secondary windings in series with said two outgoing conductors, condensers in series with said incoming conductors, the windings of said repeating coil and the condensers having such electrical characteristics that high voltage low frequency signals incoming over the incoming conductors will induce a negligible current in the secondary windings of the repeating coil and in the two outgoing conductors, and means for shunting said condensers responsive to low potential high frequency signals on said outgoing conductors to permit the free passage of said low potential high frequency signals through said repeating coil out over the incoming conductors.

10. In a transmission system, a line having two incoming conductors and two outgoing conductors, a repeating coil having primary windings in series with said two incoming conductors and secondary windings in series with said two outgoing conductors, condensers in series with said incoming conductors, the windings of said repeating coil and the condensers having such electrical characteristics that high voltage low frequency signals incoming over the incoming line conductors will induce a negligible current in the secondary windings of the repeating coil and in the two outgoing conductors, a relay bridged across said outgoing conductors responsive to low potential high frequency signals and means responsive to the operation of said relay for short-circuiting said condensers to permit the free passage of said low potential high frequency signals through said repeating coil out over said incoming conductors.

11. In a transmission system, a line having two incoming conductors and two outgoing conductors, a repeating coil having primary windings in series with said two incoming conductors and secondary windings in series with said two outgoing conductors, condensers in series with said incoming conductors, the windings of said repeating coil and the condensers having such electrical characteristics that high voltage low frequency signals incoming over the incoming line conductors will induce a negligible current in the secondary windings of the repeating coil and in the two outgoing conductors, resistances, and means for shunting said condensers through said resistances responsive to low potential signals of higher frequency on said outgoing conductors to permit the free passage of said low potential high frequency signals through said repeating coil and out over said incoming conductors.

12. In combination, a transmission line having line conductors, condensers in series with said line conductors, non-lineal resistance elements connected across from a point between the condensers in one conductor to a point between the condensers in the other conductor, and an inductance connected in shunt of the series condensers.

13. In combination, a transmission line having two conductors, an acoustic shock preventing means comprising condensers in series in the conductors, inductances in shunt of the condensers and non-lineal resistance elements in shunt of the conductors and connected across from a point between the condensers of one conductor to a point between the condensers of the other conductor, said elements being conductive to abnormal high potentials within the voice frequency range, said condensers being conductive to normal potentials within the voice frequency range and said inductances being conductive to lower potential ringing frequency currents.

14. In a protective device the combination with line conductors of condensers inserted in series in one of said line conductors, an inductance inserted in said line conductor in shunt of said condensers, and non-lineal resistance elements arranged for the passage of current in either direction inserted at the mid-point between said condensers and the other conductor.

15. In a. transmission system, a line, means in said line for blocking abnormally high potentials within the voice frequency range and for passing normal potentials within the voice frequency range and for passing lower potentials of ringing frequency, said means including capacity, inductance and non-lineal resistance elements of the rectifier type.

16. In a transmission line, means including capacity, inductance and non-lineal resistance for blocking abnormally high potentials within the voice frequency range and the ringing frequency range and for passing normal potentials within the voice frequency range and for passing normal potentials of the ringing frequency range incoming from either end of said means.

17. In a signaling system, an exchange, a transmission line terminating in said exchange, means including a repeating coil and condensers in series with one set of windings of said repeating coil for protecting said exchange against high potential low frequency current signals in said line, and means responsive to low potential ringing frequency current signals from the exchange for shunting said condensers to permit the free passage of said low potential ringing frequency current signals out over the line through the repeating coil.

18. In a signaling system, an exchange, a transmission line terminating in said exchange, means in said line including condensers, repeating coils and non-lineal resistance elements for protecting said exchange against abnormally high potentials within the voice frequency range and the ringing frequency range and for passing normal potentials within the voice frequency range incoming to or outgoing from the exchange and for passing normal potential ringing frequency signals from the exchange.

LANGFORD J. BOWNE. 

